AP CSP - Unit 1 Review

What is the best explanation for why digital data is represented in computers in binary?

• The binary number system is the only system flexible enough to allow for representing data other than numbers.

• It's easier, cheaper, and more reliable to build machines and devices that only have to distinguish between binary states.

• It typically takes fewer digits to represent a number in binary when compared to other number systems (for example, the decimal number system)

• It's impossible to build a computing machine that uses anything but binary to represent numbers

What is the 4-bit binary number for the decimal number Ten (10)?

• 0010

• 1010

• 0110

• 0101

What is the minimum number of bits you would need to encode the 26 letters of the alphabet plus a space - a total of 27 characters?

• 2 Bits

• 3 Bits

• 5 Bits

• 6 Bits

Number systems with different bases such as binary (base-2) and decimal (base-10) are all used to view and represent digital data.

Which of the following is NOT true about representing digital data?

• At one of the lowest levels of abstraction, all digital data can be represented in binary using only combinations of the digits zero and one.

• The same value (number) can have a different representation depending on the number system used to represent it.

• Groups of bits can be used to represent abstractions, including but not limited to numbers and characters.

• Some large numbers cannot be represented in binary and can only be represented in decimal.

Consider the following three binary numbers:

01010 010000 1110

Which of the following lists the numbers in order from least to greatest?

• 010000, 1110, 01010

• 01010, 1110, 010000

• 01010, 010000, 1110

• 1110, 01010, 010000

A middle school is expanding to open a high school next year, doubling the total number of students. The school keeps a database in which each student's unique ID number is stored as an 8 bit number called studentID. Before the arrival of the new students almost every 8 bit number has already been assigned to a student. Of the options provided below, which is the smallest change to the way studentID is represented necessary to ensure each incoming student receives a unique ID?

• Add a bit to studentID to double the number of IDs that the database can represent.

• Double the number of bits in studentID to double the number of IDs that the database can represent

• Keep using an 8-bit number for studentID but reserve the first bit to indicate middle school or high school.

• Remove a bit from studentID to make room for incoming students

8 bits is enough to represent 256 different numbers. How many total bits do you need to represent 512 (twice as many) numbers?

• 9 Bits

• 10 Bits

• 16 Bits

• 17 Bits

Two students have developed a protocol in which they send 4-bit messages to each other. They decide to modify their protocol to start sending 8-bit messages instead. How many more values can be represented in an 8-bit message than a 4-bit message?

• 2¹ = 2 times as many values

• 2²= 4 times as many values

• 2³ = 8 times as many values

• 2⁴ = 16 times as many values

A compression scheme for long strings of bits called run-length encoding is described as follows:

Rather than record each 0 and 1 individually, instead record "runs" of bits by storing the number of consecutive 1s and 0s that appear.

Since it's binary, any run of 0s must be followed by a run of 1s (even if the run is only 1-bit long) and vice versa. Thus, you can store a list of small numbers that represents the alternating runs of 0s and 1s. The image above is an example:

To uncompress the data back into its original binary state, you simply reverse the process. This technique is an example of what type of compression?

• Lossy compression

• Lossless compression

• Fast Fourier Transform compression

• Tailored compression

A raw digital sound file samples a sound wave at some interval and measures the height of the wave at each point. Thus, raw sound is recorded as a list of numbers.

In very broad terms the MP3 audio compression algorithm identifies frequencies and volume levels - low and high - that are outside the range of human hearing and removes the data representing these frequencies from the original. This technique results in a smaller audio file that sounds exactly the same to the human ear.

This technique is an example of what type of compression?

• Lossy compression

• Lossless compression

• Fast Fourier Transform compression

• Tailored compression